Dual Motive : A Sloane Merritt Missing Persons Thriller

by M.K. Quinn

A missing couple. A marriage built on secrets. And a case that will force Sloane Merritt to question everything she believes about love, loyalty… and what people are capable of hiding.

When Brantley Williams hires Atlanta private investigator Sloane Merritt to find his brother and sister-in-law, the situation doesn’t make sense. Callum and Meredith Williams vanished without a trace—no signs of struggle, no warning, no explanation.

At first glance, it looks like they left willingly.

But the deeper Sloane digs, the more disturbing the truth becomes.

The timeline doesn’t hold.

Their behavior in the weeks leading up to their disappearance was out of character.

And the life they built together begins to fracture under scrutiny.

Did they run? Were they taken? Or is one of them responsible for the other’s disappearance?

All marriages have secrets.

The small ones get overlooked.

The dangerous ones have a way of surfacing.



Meanwhile, a long-buried lead finally emerges.

David Harding has been found—and the truth behind the DNA match is finally within reach.

For the first time in twenty years, Sloane isn’t just chasing a ghost. She’s closing in on the truth about Eden Pike.

But the truth was never lost. It was hidden—on purpose.

Perfect for fans of missing persons thrillers, female-led detective series, and gripping psychological suspense, Dual Motive takes the investigation deeper than ever—where every relationship hides a secret… and the truth about Eden Pike is closer than it’s ever been.

220 pages, Kindle Edition

Published June 8, 2026

About the author

M.K. Quinn is a Georgia-based author, armchair detective, and lifelong observer of the shadows between ordinary life and the mysteries that lurk beneath it. A self-professed missing-persons obsessive, she has spent years studying real cases, investigative techniques, and the emotional toll of unresolved disappearances—passions that fuel every page of the Sloane Merritt Missing Persons Series. When she’s not writing twisty, character-driven thrillers, M.K. lives in Atlanta with her endlessly supportive husband and their three mischievous cats, who firmly believe they’re her true co-authors. The Sloane Merritt Series is her debut, marking the beginning of a dark, compelling universe built for readers who love smart heroines, layered mysteries, and stories that refuse to let go.

Reviews

[Sara E · Rating 5 out of 5]

4.5 rounded up!

I really enjoyed this installment of the series. Sloane and Theo advance in their relationship, there is news about Eden, and Sloane’s latest case is fascinating!

I continue to enjoy the characters, the writing is delightful, and I really enjoyed the setting!

I received an advance review copy for free, and I am leaving this review voluntarily.

[Terri | Twist & Doubt | Bookstagram · Rating 4 out of 5]

When a married couple disappears without a trace, private investigator Sloane Merritt is hired to uncover what happened. But as she digs deeper, the cracks in their seemingly perfect marriage begin to show, and what starts as a missing persons case quickly becomes something far more complicated.

The sixth instalment in the Sloane Merritt Missing Persons Thrillers series was a ride. I spent most of the book wondering what on earth is actually going on. The tension never really let up, and the stakes felt high from beginning to end, and the ongoing mystery as to Sloane’s childhood friend Eden’s whereabouts hits a sharp note at the end of this book.

I love where Sloane and Theo are at in their relationship. It feels refreshingly realistic, and they’re both so emotionally mature in the way they communicate and support one another. It’s a nice contrast to the chaos of the investigations.

Ash is still my MVP. She radiates badass girl-boss energy, steals every scene she’s in, and I’d happily read an entire spin-off centred around her.

There were a few continuity hiccups that caught my attention, and I found the ending a little too neat and convenient for my liking. That said, I still had a great time with this one. Books 3 and 5 remain my favourites of the series, but this was another entertaining mystery that kept me hooked and second-guessing myself.

If you’re already invested in Sloane Merritt’s journey, this is absolutely one worth adding to your TBR.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Rachel Boyd · Rating 5 out of 5]

I've read every book in this series and it's quickly becoming a favorite of mine. The series follows Sloane, a private investigator who helps find missing persons, while also trying to solve the disappearance of her best friend, who disappeared when she was 15.

I loved the main characters. Sloane is tough, smart, and she cares so much about people. Theo is smart, supportive, and a solid partner. Ash is amazing as a friend and at her job. I like that she has been a more common presence in the books.

So, this case was twisting and turning all over the place. It was so interesting and had so many red herrings. A lot to the case, a lot of places it could have gone. I was thoroughly entertained. I also like that the victims and perpetrators aren't always the best people, but Sloane fights for them anyway. People are imperfect, but that doesn't mean they deserve awful things to happen. I like that these books can get me thinking and aren't always black and white, as is the case with many true crime stories. I was fortunate enough to get an advanced copy of this book; I'm such a fan of this series and the author. I love the author's writing style and story telling. I am so excited to see what is next in the series and if we finally get a conclusion regarding Eden.

[Jodi · Rating 4 out of 5]

This is my first Sloane Merritt book.

I enjoyed that there wasn't much 'fluff' or drama in this story. The twists are there, but the lead-up to them isn't overwhelmingly drastic.

Sloane is a confident PI.
Ash is a competent co-worker.
Theo is a great partner to Sloane.
They all mesh well.

The discoveries are well delivered. Each scene and situation is described with the right amount of info! I appreciated that the PI plot isn't intertwined with Sloane's personal plot. I like that the PI missing-persons case made up the majority of the book, and then Sloane's missing-persons case got its own time to shine as well.

The only thing that felt off about this book is that there was some repetition, and the plot doesn't have anything specific to make it truly unique against similar plots in similar stories.

Overall, I really enjoyed the book. Sloane is an interesting character, and I will be seeking out the previous books now that I've finished this one.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Mary Ryan · Rating 4 out of 5]

In this cracking read, Sloane is hired to find a man's brother and wife who have disappeared. They seem to have disappeared without a trace and it is clear from their house that a serious fight occurred. Their boat is also missing and it seems that each of them were not very nice people and had various secrets.

I like this series as it doesn't matter if the missing person is nice or not. Sloane treats each case equally and is always focused on the task at hand. There are plenty of twists throughout this story as Sloane and Theo finally get the answers surrounding this disappearance. The book wraps up nicely with events linked to her friend Eden's disappearance and a major breakthrough comes at the end albeit with a surprise and more questions. Can't wait to find out more in the next book. It can't come soon enough.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Lorelei Tomlinson · Rating 4 out of 5]

I enjoyed reading this book. The primary story is about a missing couple and the investigation that follows. There is also a continuation of the secondary story about Sloane's search for Eden. You don't need to have read the previous books in the series to follow the story in Dual Motive.

This story kept me guessing about what had happened to the missing couple. There was lots of suspense. The story and characters were easy to follow. The writing style was concise and provided important details without going on and on about irrelevant things.

If you like suspenseful stories, you may want to read this one.

I received a free advance reader copy of this book. The opinion that I express is my own.

[Mary · Rating 4 out of 5]

Sloane, Theo and Ash are at it again, this time, trying to get to the bottom of the disappearance of a couple. Between the business partners, the significant others of the extramarital affairs and the couples own volatile relationship, there are many suspects, but will the couple be found alive?

On top of this, Sloane is still stung by the DNA results she has received regarding Eden.

Somehow, Sloane is always able to put this to the back of her mind and solve her cases, but still wondering what happened to Eden. Morrison has more news for Sloane, and she wants Sloane there. In the end, are we closer, maybe, but we have more questions. Now I am looking forward to #7 in the series.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Bette Reith · Rating 4 out of 5]

Another great installment of the Sloane mystery series. This one involves a couple who have been missing for over a week. The local police shrug it off as they are adults, perhaps on a getaway. Sloane is hired by a brother, who says the absence is not normal; he would never leave without saying something.

As she starts talking to different people in their lives, a timeline is formed, but things do not line up. The couple had many secrets to hide, but they may have some they were hiding from each other.

This series is great. I love the characters and how things get pieced together. Sometimes the self-reflection is a bit much, but overall, it's a quick and fun read. Thanks to BookSirens for the ARC of this book.

[Danielle · Rating 5 out of 5]

I have read all the books in Sloane Merritt's missing person series and loved them all. This story was a suspenseful read tracking down a missing married couple. The twists and many turns kept me reading. This was a 2 sitting read it had me hooked from the start. The continuing saga of Sloane's missing friend from childhood, Eden had its own twist and turns that left me shocked and wanting more answers. I can't wait to read the next book in the series!!

This was a complimentary ARC copy that I reviewed honestly and voluntarily.

[Gisela Marengo · Rating 4 out of 5]

This book was given to me by BookSirens as an ARC here is my voluntarily review. 4.50⭐️ I have been following this series. I found myself emotionally invested in their journey, desperately hoping they would find answers while bracing myself for what might come next. Every revelation hit harder than I expected, and more than once I found myself stopping to process what had just happened. Just when I thought I knew where the story was heading, another twist shattered my assumptions and left me reeling.I can’t wait for book 7 I need to know what happened to Eden 😱.

[Joyclyn · Rating 5 out of 5]

Another enjoyable Sloane Merritt Mystery. The list of suspects involved in the disappearance of Meredith and Collum kept growing and kept me guessing throughout the book. I also liked that the Eden storyline took more of a backseat to the overall plot this time.

I am enjoying the slow simmer between Theo and Sloane and look forward to seeing where their relationship goes next. Likewise, I want closure on Eden.

I love the pace of these books!

Thank you BookSirens for the advanced copy of this book and allowing me to give my review!

[Jeri · Rating 4 out of 5]

The sixth book in this series has a different style of investigation- 2 missing people, multiple possible suspects. Our FMC, Sloane Merritt, has a good crew helping her-Ash the computer genius, and Theo, her cop “boyfriend.” Great descriptions of weather and water, wonderful secondary characters described in gritty detail. And at the end, as usual, we are treated to a little more of the Eden case. I received the ARC of this excellent novel from BookSirens and the author, but all opinions are my own.

[Sandy Goguen-Young · Rating 5 out of 5]

I have read all the books in the series. Sloane investigates missing people, I loved the twist and turns of the missing married couple, in this story. As always finding answers to the disappearance of her childhood best friend after 20 years. I love how the author gives you one more piece of the puzzle to solving the mystery and leaves you anxiously wanting to read the next book.

Thank you Book Sirens for this ARC book and I am leaving this honest review voluntarily.

[Carol Stefanik · Rating 5 out of 5]

If you are into the Sloane Merritt stories you will like this one. We can feel the relationship with Theo growing in the right ways. Can't say anything about Eden's case without a spoiler alert. I will admit I expected a different character to be the bad guy.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Fatima Salih · Rating 4 out of 5]

I have been following Sloane as she hopes to uncover what happened to her good friend, Eden while she takes on cases to help friends and family get answers. I love how each story show how dedicated Sloane is to her craft and how each storyline gets better and even more interesting.

I received an advance review copy for free, and I am leaving this review voluntarily.

[Lynseygibs · Rating 4 out of 5]

Thanks to BookSirens, publishers and author for an ARC of Dual Motive.

A great addition to the Sloane Merritt series, with the continuing mystery regarding Eden deepening. Roll on the next installment

[Terry · Rating 3 out of 5]

Good story only because I am 'hooked' on knowing the ending of the base story line - the writing is not as detailed as it was at the beginning which is disappointing.

[Farah Rk · Rating 4 out of 5]

I wish to thank the author for the ARC. As always, the series keeps readers hooked until the very end, leaving us craving more. Enjoyed it.